Angiotensin II regulates endothelial cell migration through calcium influx via T-type calcium channel in human umbilical vein endothelial cells

In vivo bioresorbability and bone formation ability of sintered highly pure calcium carbonate granules

Calcium carbonate-based bone substitutes derived from natural coral exoskeleton (aragonite) are resorbed and remodeled faster than calcium phosphate-based substitutes. However, coral species with structures appropriate for use as bone substitutes are very limited. Therefore, it is important to evaluate potential of artificial calcium carbonate ceramics as a bone substitute. In this study, calcium carbonate granules with various porosities and pore sizes were prepared by sintering a highly pure (>99.98%) calcium carbonate powder (calcite), and their resorption properties and bone formation abilities were examined in vivo for the first time. The sintered calcium carbonate was resorbed faster than β-tricalcium phosphate, which has a similar structure. However, sintered calcium carbonate did not promote new bone formation during long-term implantation. Furthermore, both resorption and new bone formation were affected by the pore structure. The optimal structures of the artificially sintered calcium carbonate bone substitute were also discussed.

Ang II-AT2R increases mesenchymal stem cell migration by signaling through the FAK and RhoA/Cdc42 pathways in vitro

Background

Mesenchymal stem cells (MSCs) migrate via the bloodstream to sites of injury and are possibly attracted by inflammatory factors. As a proinflammatory mediator, angiotensin II (Ang II) reportedly enhances the migration of various cell types by signaling via the Ang II receptor in vitro. However, few studies have focused on the effects of Ang II on MSC migration and the underlying mechanisms.

Methods

Human bone marrow MSCs migration was measured using wound healing and Boyden chamber migration assays after treatments with different concentrations of Ang II, an AT1R antagonist (Losartan), and/or an AT2R antagonist (PD-123319). To exclude the effect of proliferation on MSC migration, we measured MSC proliferation after stimulation with the same concentration of Ang II. Additionally, we employed the focal adhesion kinase (FAK) inhibitor PF-573228, RhoA inhibitor C3 transferase, Rac1 inhibitor NSC23766, or Cdc42 inhibitor ML141 to investigate the role of cell adhesion proteins and the Rho-GTPase protein family (RhoA, Rac1, and Cdc42) in Ang II-mediated MSC migration. Cell adhesion proteins (FAK, Talin, and Vinculin) were detected by western blot analysis. The Rho-GTPase family protein activities were assessed by G-LISA and F-actin levels, which reflect actin cytoskeletal organization, were detected by using immunofluorescence.

Results

Human bone marrow MSCs constitutively expressed AT1R and AT2R. Additionally, Ang II increased MSC migration in an AT2R-dependent manner. Notably, Ang II-enhanced migration was not mediated by Ang II-mediated cell proliferation. Interestingly, Ang II-enhanced migration was mediated by FAK activation, which was critical for the formation of focal contacts, as evidenced by increased Talin and Vinculin expression. Moreover, RhoA and Cdc42 were activated by FAK to increase cytoskeletal organization, thus promoting cell contraction. Furthermore, FAK, Talin, and Vinculin activation and F-actin reorganization in response to Ang II were prevented by PD-123319 but not Losartan, indicating that FAK activation and F-actin reorganization were downstream of AT2R.

Conclusions

These data indicate that Ang II-AT2R regulates human bone marrow MSC migration by signaling through the FAK and RhoA/Cdc42 pathways. This study provides insights into the mechanisms by which MSCs home to injury sites and will enable the rational design of targeted therapies to improve MSC engraftment.

Endotoxin-induced vascular endothelial cell migration is dependent on TLR4/NF-κB pathway, NAD(P)H oxidase activation, and transient receptor potential melastatin 7 calcium channel activity

Endothelial dysfunction is decisive and leads to the development of several inflammatory diseases. Endotoxemia-derived sepsis syndrome exhibits a broad inflammation-induced endothelial dysfunction. We reported previously that the endotoxin, lipopolysaccharide (LPS), induces the conversion of endothelial cells (ECs) into activated fibroblasts, showing a myofibroblast-like protein expression profile. Enhanced migration is a hallmark of myofibroblast function. However, the mechanism involved in LPS-induced EC migration is no totally understood. Some studies have shown that the transient receptor potential melastatin 7 (TRPM7) ion channel is involved in fibroblast and tumor cell migration through the regulation of calcium influx. Furthermore, LPS modulates TRPM7 expression. However, whether TRPM7 is involved in LPS-induced EC migration remains unknown. Here, we study the participation of LPS as an inducer of EC migration and study the mechanism underlying evaluating the participation of the TRPM7 ion channel. Our results demonstrate that LPS induced EC migration in a dose-dependent manner. Furthermore, this migratory process was mediated by the TLR-4/NF-κB pathway and the generation of ROS through the PKC-activated NAD(P)H oxidase. In addition, LPS increased the intracellular calcium level and the number of focal adhesion kinase (FAK)-positive focal adhesions in EC. Finally, we demonstrate that using TRPM7 blockers or suppressing TRPM7 expression through siRNA successfully inhibits the calcium influx and the LPS-induced EC migration. These results point out TRPM7 as a new target in the drug design for several inflammatory diseases that impair vascular endothelium function.

Functional properties of ion channels and transporters in tumour vascularization

Vascularization is crucial for solid tumour growth and invasion, providing metabolic support and sustaining metastatic dissemination. It is now accepted that ion channels and transporters play a significant role in driving the cancer growth at all stages. They may represent novel therapeutic, diagnostic and prognostic targets for anti-cancer therapies. On the other hand, although the expression and role of ion channels and transporters in the vascular endothelium is well recognized and subject of recent reviews, only recently has their involvement in tumour vascularization been recognized. Here, we review the current literature on ion channels and transporters directly involved in the angiogenic process. Particular interest will be focused on tumour angiogenesis in vivo as well as in the different steps that drive this process in vitro, such as endothelial cell proliferation, migration, adhesion and tubulogenesis. Moreover, we compare the 'transportome' system of tumour vascular network with the physiological one.

Blockade of the intermediate-conductance Ca(2+)-activated K+ channel inhibits the angiogenesis induced by epidermal growth factor in the treatment of corneal alkali burn

Epidermal growth factor (EGF) is used to treat alkali-burned corneas. However, EGF-induced corneal angiogenesis, which is currently untreatable, is a side effect of this therapy. We therefore explored the role of the intermediate-conductance Ca(2+)-activated K(+) channel (KCa3.1) in EGF-induced angiogenesis and tested whether KCa3.1 blockade can suppress EGF-induced corneal angiogenesis. The proliferation, migration and tube formation of HUVECs (human umbilical vein endothelial cells) in response to EGF, the MEK inhibitor PD98059 and the KCa3.1 inhibitor TRAM-34 were analyzed in vitro via MTT, cell counting, scratch and tube formation assays. The protein and mRNA levels of KCa3.1, phosphorylated-ERK (P-ERK), total-ERK (T-ERK), cyclin-dependent kinase 4 (CDK4), vimentin and MMP-2 were assessed via western blotting and RT-PCR. KCa3.1 and vimentin expression were also detected through immunofluorescence staining. Flow cytometry was performed to examine the cell cycle. Further, an in vivo murine alkali-burned cornea model was developed and treated with EGF and TRAM-34 eye drops to analyze the effect of these treatments on corneal healing and angiogenesis. The corneas were also analyzed by histological staining. The in vitro results showed that EGF induces the upregulation of KCa3.1 and P-ERK in HUVECs and that this upregulation is suppressed by PD98059. EGF stimulates proliferation, migration and tube formation in HUVECs, and this effect can be suppressed by TRAM-34. TRAM-34 also arrests HUVECs in the G1 phase of the cell cycle and downregulates CDK4, vimentin and MMP-2 in these cells. The in vivo results indicated that TRAM-34 suppresses EGF-induced corneal angiogenesis without affecting EGF-induced corneal wound healing. In summary, the upregulation of KCa3.1 may be crucial for EGF-induced angiogenesis through the MAPK/ERK signaling pathway. Thus, KCa3.1 may be a potential target for the treatment of EGF-induced corneal angiogenesis.

Calcium in tumour metastasis: new roles for known actors

In most cases, metastasis, not the primary tumour per se, is the main cause of mortality in cancer patients. In order to effectively escape the tumour, enter the circulation and establish secondary growth in distant organs cancer cells must develop an enhanced propensity to migrate. The ubiquitous second messenger Ca²⁺ is a crucial regulator of cell migration. Recently, a number of known molecular players in cellular Ca²⁺ homeostasis, including calcium release-activated calcium channel protein 1 (ORAI1), stromal interaction molecule 1 (STIM1) and transient receptor potential (TRP) channels, have been implicated in tumour cell migration and the metastatic cell phenotype. We discuss how these developments have increased our understanding of the Ca²⁺ dependence of pro-metastatic behaviours.

Adenosine monophosphate-activated kinase alpha1 promotes endothelial barrier repair

The vascular endothelium responds to damage through activation of multiple signaling events that restore cell-cell adhesion and vascular integrity. However, the molecular mechanisms that integrate these events are not clearly defined. Herein, we identify a previously unexpected role for adenosine monophosphate-activated protein kinase (AMPK) in pulmonary microvascular endothelial cell (PMVEC) repair. PMVECs selectively express the AMPKα1 catalytic subunit, pharmacological and short hairpin RNA-mediated inhibition of which attenuates Ca(2+) entry in these cells induced by the inflammatory Ca(2+)-signaling mimetic thapsigargin. We find that AMPKα1 activity is required for the formation of PMVEC cell-cell networks in a prorepair environment and for monolayer resealing after wounding. Decreasing AMPKα1 expression reduces barrier resistance in PMVEC monolayers, results consistent with a role for AMPKα1 in cell-cell adhesion. AMPKα1 colocalizes and coimmunoprecipitates with the adherens junction protein N-cadherin and cofractionates with proteins selectively expressed in caveolar membranes. Assessment of permeability, by measuring the filtration coefficient (K(f)) in isolated perfused lungs, confirmed that AMPK activation contributes to barrier repair in vivo. Our findings thus provide novel evidence for AMPKα1 in Ca(2+) influx-mediated signaling and wound repair in the endothelium.

Skeletal muscle-endothelial cell cross talk through angiotensin II

The role of angiotensin II (ANG II) in postnatal vasculogenesis and angiogenesis during skeletal muscle (SKM) regeneration is unknown. We examined the capacity of ANG II to stimulate capillary formation and growth during cardiotoxin-induced muscle regeneration in ACE inhibitor-treated ANG II type 1a receptor knockout (AT1a−/−) and C57Bl/6 control mice. Analysis of tibialis anterior (TA) cross-sections revealed 17% and 23% reductions in capillarization in AT1a−/− and captopril treated mice, respectively, when compared with controls, 21 days postinjury. Conversely, no differences in capillarization were detected at early time points (7 and 10 days). These results identify ANG II as a regulator of angiogenesis but not vasculogenesis in vivo. In vitro angiogenesis assays of human umbilical vein endothelial cells (HUVECs) further confirmed ANG II as proangiogeneic as 71% and 124% increases in tube length and branch point number were observed following ANG II treatment. Importantly, treatment of HUVECs with conditioned media from differentiated muscle cells resulted in an 84% and 203% increase in tube length and branch point number compared with controls, which was abolished following pretreatment of the cells with an angiotensin-converting enzyme inhibitor. The pro-angiogenic effect of ANG II can be attributed to an enhanced endothelial cell migration because both transwell and under agarose migration assays revealed a 37% and 101% increase in cell motility, respectively. Collectively, these data highlight ANG II as a proangiogenic regulator during SKM regeneration in vivo and more importantly demonstrates that ANG II released from SKM can signal endothelial cells and regulate angiogenesis through the induction of endothelial cell migration.